This invention relates to a reflow soldering apparatus for soldering parts which are temporarily fixed on a substrate by means of cream solder.
Reflow soldering techniques have been used tp solder electrical parts on a substrate by applying heat to melt and re-solidify (reflow) the cream solder used to temporarily fix the electrical parts on the substrate. A conventional open-type reflow soldering apparatus employs a hot iron plate to reflow the cream solder when the substrate is moved in contact with the hot iron plate. However, such a conventional apparatus presents several difficulties. First, if the substrate is curved or deformed to such an extent that it has a portion lifted off the hot iron plate, an additional process is required to flaten the substrate by means of a suitable flattening tool in order to avoid insufficient soldering. Second, the apparatus cannot be used in soldering parts having lead wires which extend from the substrate to lift off the substrate from the hot iron plate.
In order to avoid these difficulties, it has been proposed to move the substrate in an atmosphere of hot gas created in a heating furnace. However, this soldering technique cannot be used when soldering is required only for a part of the substrate or when the parts are thermolabile. In addition, it provides a great degree of thermal stress which degraded the reliability of the parts, particularly after reflowing twice.